1. Field of the Invention
The present invention relates to a pre-process which expels the oxygen in the deionized water, DI water, before preparing the displacement plating solution for copper interconnects grown by displacement reaction, and more particularly by electrochemical displacement deposition (EDD).
2. Description of Related Art
There have been many methods of growing copper films or interconnects for circuits of very large scale integration (VSLI) and ultra large scale integration (ULSI). They can be classified into physical vapor deposition (PVD), chemical vapor deposition (CVD), electroplating, and electroless deposition, etc. However, there are several disadvantages found in these methods. In the case of PVD, the stop coverage of the copper grown in the grooves on the surface of the wafer is not even. The copper film grown by CVD can be conformal while it contains too many impurities such that it has a very high resistance. Furthermore, the popular dry etching process cannot be adopted to remove the unwanted copper due to the corresponding product is non-volatile and is not easily exhausted out of the wafer. Currently, the Damascene process and its variations are predominantly used to form copper wires for modern integrated circuits (ICs).
The Damascene process utilizes the chemical-mechanical polish (CMP) process to remove the unwanted portion of copper. However, the process steps are complicate and the throughput is low. Some researchers proposed low-cost the methods such as electroplating and electroless deposition to increase the throughput. However, there was a concern about the plating agents which will pollute the products and the environment. And the obtained resistance, the step coverage and the quality of the grown copper still need to be improved.
The electrochemical displacement deposition (EDD) has been proposed recently to grow copper with a solution containing popular chemicals used in IC fabrication processes. The EDD process is utilized as a pre-process to create a seed layer for later growth of thick copper layers by the electroplating method or the electroless deposition. However, the copper grown by the method of the EDD also has a high resistance and is difficult to adhere on the surface of the wafer. An annealing process is usually used to reduce the resistance of the copper film.
The present invention has arisen to mitigate and/or obviate the possibility of high resistance for the copper obtained in the chemical plating method, especially the EDD method.